The material is said to change its appearance, texture and shape in response to environmental stimuli, and can be used to encrypt or decrypt information.
Scientists at Pennsylvania State University, USA, have developed a programmable ‘smart skin’ material from a hydrogel. This could open new possibilities for adaptive camouflage and soft robotics.
The work was inspired by cephalopods such as octopuses, which can dynamically alter their skin’s colour and texture to camouflage themselves or communicate with each other. “Cephalopods use a complex system of muscles and nerves to exhibit dynamic control over the appearance and texture of their skin,” says Assistant Professor Hongtao Sun at the university. “Inspired by these soft organisms, we developed a 4D-printing system to capture that idea in a synthetic, soft material.”
Halftone-encoded 4D printing of stimulus-reconfigurable binary domains for cephalopod-inspired synthetic smart skins, published in Nature Communications, describes how the material is made using halftone-encoded 4D printing.
This adds the fourth dimension of time to conventional 3D printing, producing structures capable of changing shape, properties, or functionality over time when exposed to external triggers such as heat, mechanical forces or solvents.
Similar to the dot patterns used in printed images, halftone printing allows digital information to be embedded directly into the material. It translates graphic or textural data onto a surface in the form of binary ones and zeros.
This approach can encode binary instructions across the hydrogel surface that determine how diff erent regions respond to external stimuli. Some regions swell, soft en, or contract more than others when the environment changes, enabling the material to morph into new shapes or reveal hidden patterns when exposed to specific stimuli.
To demonstrate the concept, a hidden image of the Mona Lisa has been encoded into the hydrogel film.
When the film is washed with ethanol, the material appears transparent. However, when it is exposed to cold water, heat, or mechanical stretching, the image emerges. The encoded information can also be revealed through digital image correlation, which measures deformation patterns as the material is stretched.
Beyond visual effects, the design enables coordinated control of multiple properties within a single material. By adjusting the halft one pattern, the researchers say they can simultaneously programme optical appearance, mechanical behaviour, surface texture and shape morphing. The hydrogel sheets can also transform from flat films into complex 3D shapes without the need for multiple layers or different materials.
The team encoded the Mona Lisa image directly into flat films that later emerged as the material transformed into 3D shapes.
This multifunctional behaviour could be harnessed for adaptive camoufl age surfaces, secure information storage, biomedical devices and soft robotic components that respond dynamically to their surroundings.
The team will focus on developing scaleable fabrication methods and expanding the range of responsive behaviours encoded within the hydrogel structures.
Extracted from IOM3 website - read more here